Conventional internal combustion engines have fuel systems including a fuel tank, fuel filter, fuel pump and carburetor. The fuel pump pumps fuel from the fuel tank through the fuel filter (which removes foreign matter from the fuel) to the carburetor, which controls delivery of the fuel to the engine intake manifold. The inventor has found that the fuel economy of such systems may be improved by pressurizing and vapourizing the fuel before it reaches the carburetor. For example, a 1984 Ford Sierra station wagon having a two liter engine modified in accordance with the invention was driven 169.5 miles, during which the vehicle consumed 3.4 gallons of gasoline, thereby achieving 49.85 miles per gallon. The modifications of the invention were removed and the same vehicle was then driven a further 168 miles over the same terrain covered by the modified vehicle, during which time the vehicle consumed 6.1 gallons of gasoline, thereby achieving only 27.54 miles per gallon. As another example, a 360 cubic inch Dodge Charger engine modified in accordance with the invention achieved 23 miles per gallon in consuming a measured amount of gasoline, while coupled to a dynamometer. The same engine achieved only 13 miles per gallon in consuming the same measured amount of gasoline and operating under the same conditions, after the modifications of the invention were removed.